1. Field of the Invention
The invention relates in general to a polymeric compositions containing reinforcement fibers, and a process for the preparation thereof, which products are useful for the formulation of reinforced structures, coatings, liners, and the like. The invention is also directed to an apparatus for and a method of spraying this polymeric compositions, both in the form of a film and a foam.
2. Description of Related Art
A strong, durable, high build rate coating with no volatile organic compound (VOC) emissions has been desired as a protective coating for many years. Attempts at producing a coating having those characteristics has resulted in compromising one or several of desired properties. Polyurethane polymers, and coatings made from them, result from the reaction of an isocyanate having an isocyanate terminated compound and a polyol having an hydroxyl terminated compound. Polyurethane foams are typically produced by reaction of the polyisocyanate with the polyol in the presence of a blowing agent. Historically, chlorofluorocarbons such as CFC-11 have been the blowing agents of choice. These agents have been thought to negatively affect the environment and are being phased out of the polyurethane foam manufacture.
Low density coatings, when fabricated, tend to have low toughness or abrasion resistance. Furthermore, most coatings require a significant amount of organic solvent to carry the coating during spraying applications, which contributes significantly to the problem of volatile organic compounds (VOC) emissions. Coating compositions must meet with Occupational Safety and Health Administration and the Environment Protection Agency requirements. Since VOCs are typically toxic, smog-producing and noxious, their continued release can cause a detrimental impact on worker safety and on the environment. Governmental regulations restrict the amounts and types of VOCs which are permitted to escape into the atmosphere from coating compositions, therefore, there should preferably be no amount of organic solvents present in coating compositions.
Thick coatings tend to be spongy or brittle and applying that type of coating to a vertical surface is a slow and tedious process due to slumping problems or curing/out gassing times required. The majority of low VOC coatings available at the present time are only acceptable for thin coating applications (less than 20 mils dry film thickness), or have an exceedingly long dry time between applications which prohibits the successful fabrication of high build rate and/or thick coatings. Another disadvantage associated with many of the products prepared in the prior art having high viscosities is that application by spraying is often precluded.
Polymeric resins containing fillers are known, and are described in U.S. Pat. No. 5,604,266 to Mushovic. Mushovic discloses a polyester-polyurethane resin material mixed with at least a KEVLAR® filler (manufactured by DuPont). The KEVLAR pulp filler is added to the polyol reactant of the polyurethane. The polyurethane mixture of Mushovic was then poured into a mold. Mushovic does not disclose or suggest a sprayable polymeric composition containing reinforcing fibers. In the present invention, polymer compositions containing KEVLAR or other reinforcing fibers can be sprayed, while maintaining homogeneity of the composition, necessary for the spray application. Polymer compositions that can be sprayed are more flexible in the field, they can conform to complex shapes and surface details. In order to spray a polymeric composition comprising a reinforcing fiber, such as KEVLAR, SPECTRA® (owned and manufactured by Allied-Signal, Inc., Delaware, U.S.A.), carbon fullerenes and nanotubes, not only must the composition be mixed properly but also requires a modification be made to the dispensing apparatus, i.e. the spray gun. U.S. Pat. No. 4,857,569 to Cotts et al., discloses a polymer alloy composition prepared by intimately mixing one or more polyurethane components with selected reinforcing amounts of rod-like aromatic polyamide components (e.g. KEVLAR). However, the compositions of Cotts must be formed either by blending two individual solutions of the polyurethane and rod-like polyamide components in a common or mutually compatible solvent, or by polymerizing the polyurethane components in a solvent, which is itself a solution of the rod-like polyamide component in a suitable solvent. Thus, the KEVLAR reinforcing fiber must be dissolved in a solvent, e.g., a solution of polyparaphenyleneterephthalamide. U.S. Pat. Nos. 4,599,401; 4,629,779; 4,707,535; and 4,725,653 to Koleske; U.S. Pat. No. 4,857,579 to Domeier and U.S. Pat. No. 4,233,205 to O'Connor disclose polyurethane elastomers or other polyurethane products containing KEVLAR fibers. U.S. Pat. No. 5,610,224 to DePue et al., discloses an elastic and high strength material formed from polyurethane and aromatic polyamide. Japanese Patent 53-34884 to Masanobu et al., discloses a composite material prepared by curing and bonding an aromatic polyamide fiber and a thermosetting resin with a specific lactam compound and an isocyanate compound.
A hybrid liner is described in U.S. Pat. No. 4,956,397 to Rogowski et al., which describes an insulating solid rocket liner made from polyurethane rubber and KEVLAR pulp or fibers, specifically fibrillated fibers. U.S. Pat. Nos. 4,034,138 and 4,095,404 to Babayan and U.S. Pat. No. 5,120,905 to Cousin et al., all disclose polyurethane material impregnated or coated with aromatic polyamide fibers. U.S. Pat. No. 5,167,352 to Robbins and U.S. Pat. No. 5,419,139 to Blum et al., both disclose a double wall tank system or a composite cryogenic tank coated or lined with polyurethane and KEVLAR. Blum specifically discloses a tank lined with a laminate of film layers, each having a vacuum deposited metalized coating.
A problem associated with adding a reinforcing fiber, such as KEVLAR, to a polyurethane resin solution has been that the fibers separate out from the polyurethane reaction components, or deteriorate because of the solvents or catalysts in the reaction components, making it impossible to exhibit the intended properties and strength and stability of the added reinforcing fibers. Accordingly, it has conventionally been necessary to agitate the reaction components so as to be uniformly mixed and dispersed, before its use, i.e., before the polyisocyanate and polyol components are mixed together to cause the reaction. Thus, polyurethane resin formed from conventional polyurethane reaction components containing reinforcing fibers cannot be sprayed.
Conventional spray gun assemblies have spring loaded check valves for restricting the flow of two-part reactive polymers. See FIGS. 1 and 2. U.S. Pat. No. 5,810,254 to Kropfield, which describes two premixing chambers, that receive the polymer reaction components, each chamber having an actuating valve for controlling the flow of the components through the premixing chambers. Since two part polyurethanes require a very specific percentage ratio of the two material components, any significant variation will not produce a polyurethane with the desired cure effectively or quickly, and may not have the desired durability.
The ideal polymer for use as a coating or liner would contain reinforcing fibers and other fillers that could be sprayed, would be easy to use, quick to activate, and have a long service life. Polymers that do not have any volatile organic content and do not leak hazardous materials, having zero toxicity, are also necessary for use in coatings and liners. New methods for greatly reducing or eliminating VOCs during the application of such coatings are urgently needed to prevent worker injury and comply with current and pending environmental regulations. Also of great importance is the cost, performance and durability of such polymer formulations. Currently, there does not exist a method of making a polymer composition that satisfies all these criteria.